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Roadside breath tests: What you should know


Roadside breath tests: What you should know

On behalf of Patrick T. McNally, Attorney at Law | 
February 18, 2020

When a law enforcement officer asks you to submit to a roadside breath test, you may feel anxious and alarmed. Facing a driving while driving charge is daunting and overwhelming. You may think that the reading obtained from the breath test device is enough to charge and convict you of a DUI. There are some things to keep in mind when evaluating the accuracy of breath test devices

Studies from the State University of New York at Potsdam found that blood alcohol content levels obtained from breath test devices differed from those obtained from actual blood tests by at least 15%. This discrepancy may be enough to wrongfully charge someone with a DUI. In fact, one in four people who take a roadside breath test will have inflated results. 

The machines obtain blood alcohol content levels by detecting methyl structures in exhaled breath samples. There are other substances that also have methyl structures that the breath test devices may detect, including the following: 

  • Temperature and relative humidity of the air 
  • Smoke, fumes and dirt in the air 
  • Fumes from cleaners, gasoline and cigarettes 
  • Residual blood, vomit, food and drink left in the mouth 

In one test, a subject was asked to apply contact cement for an hour, then gave an exhaled breath sample 20 minutes later. The subject’s BAC level read 0.12, which is over the legal limit, even though he did not consume any alcohol. 

Other issues arise, such as whether law enforcement officers have calibrated the devices properly and routinely. Furthermore, the officer administering the test must know how to use the device correctly. Law enforcement should consider all of these factors before charging someone with a DUI. 

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